{
"cells": [
{
"cell_type": "markdown",
"id": "e9e769f4-6300-44e1-932c-33ed90197469",
"metadata": {},
"source": [
"# PLC2026 Lecture 07, 29 Jan 2026"
]
},
{
"cell_type": "markdown",
"id": "025c8646-d118-4728-ae2d-fb608bb4e970",
"metadata": {},
"source": [
"### Rust\n",
"- Rust resources: \n",
"- Installing Rust: \n",
"- Documentation: "
]
},
{
"cell_type": "markdown",
"id": "26e98d67-edec-4562-97fd-e248fdbb20db",
"metadata": {},
"source": [
"### Typing\n",
"- Static (Java, Haskell) vs dynamic (Python)\n",
" - Ideally, type errors should be caught at compile-time (static)\n",
" - Dynamic --- type is determined by current value, type of a variable can change over time\n",
"- Implicit (Haskell, Python) vs explicit (Java declarations)\n",
" - Implicit + static $\\Longrightarrow$ type inference\n",
"- Degrees of strictness\n",
" - Is mixed mode arithmetic allowed? e.g., `x = 1.5 + 3`\n",
" - Can numbers be intepreted as booleans? `if len(l) { ... }`\n",
"- Rust types\n",
" - Static\n",
" - Mostly implicit, but *must* declare types for function signatures\n",
" - **Very** strict!"
]
},
{
"cell_type": "markdown",
"id": "1de6dfb3-dfe2-43c7-9657-f804d1bb1ddb",
"metadata": {},
"source": [
"### Rust program\n",
"- **Not** object oriented\n",
"- Program is a collection of functions\n",
"- Execution begins with `main()`\n",
"- Read documentation about how to compile\n",
"- `cargo` to build Rust projects"
]
},
{
"cell_type": "markdown",
"id": "fd4f613d-981f-491d-b067-1cb793324f94",
"metadata": {},
"source": [
"### Hello world!"
]
},
{
"cell_type": "code",
"execution_count": 2,
"id": "b3625b88-45f3-4567-b209-cbc495dcba1d",
"metadata": {},
"outputs": [],
"source": [
"fn main(){\n",
" println!(\"Hello world\");\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "0018ae7e-40fd-44f6-9943-9960a3742755",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Hello world\n"
]
},
{
"data": {
"text/plain": [
"()"
]
},
"execution_count": 3,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"main()"
]
},
{
"cell_type": "markdown",
"id": "daff7b9f-e4a5-4aa5-8f8b-73a398c1dfc6",
"metadata": {},
"source": [
"- `!` after `println` signifies it is a macro, not a function --- will worry about this later\n",
"- This function returns nothing, so return value is `()`"
]
},
{
"cell_type": "markdown",
"id": "cd0a61cc-d736-405c-9fa1-0b228a1256e1",
"metadata": {},
"source": [
"### Variables\n",
"- Declare variables using `let` and assign a value\n",
"- Value implicitly fixes type"
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "7be3fe3f-2bca-4257-bd92-1b207b75619b",
"metadata": {},
"outputs": [],
"source": [
"fn var1(){\n",
" let x = 55;\n",
" println!(\"Value of x is {x}\"); // Insert value in string, Version 1\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "b0ee0bff-a3c3-4a3b-b995-5345a9329501",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of x is 55\n"
]
},
{
"data": {
"text/plain": [
"()"
]
},
"execution_count": 5,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"var1()"
]
},
{
"cell_type": "code",
"execution_count": 6,
"id": "004e4257-e464-491e-ace1-ea8949f6a0a1",
"metadata": {},
"outputs": [],
"source": [
"fn var2(){\n",
" let x = 55;\n",
" println!(\"Value of x is {}\",x); // Insert value in string, Version 2\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 7,
"id": "d76ba21a-4f8a-4fbe-9a2b-488f63c8f369",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of x is 55\n"
]
},
{
"data": {
"text/plain": [
"()"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"var2()"
]
},
{
"cell_type": "markdown",
"id": "f0f24b2a-afb5-4571-bf0b-da958f0bdf1a",
"metadata": {},
"source": [
"- What if we try to update the value of `x`?"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "abced5a0-40da-4eae-907c-97844f565fd4",
"metadata": {},
"outputs": [
{
"ename": "Error",
"evalue": "cannot assign twice to immutable variable `x`",
"output_type": "error",
"traceback": [
"\u001b[31m[E0384] Error:\u001b[0m cannot assign twice to immutable variable `x`",
" \u001b[38;5;246m╭\u001b[0m\u001b[38;5;246m─\u001b[0m\u001b[38;5;246m[\u001b[0mcommand_8:1:1\u001b[38;5;246m]\u001b[0m",
" \u001b[38;5;246m│\u001b[0m",
" \u001b[38;5;246m2 │\u001b[0m \u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249ml\u001b[0m\u001b[38;5;249me\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;54mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m5\u001b[0m\u001b[38;5;249m5\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m┬\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m╰\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m first assignment to `x`",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;68m│\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;68m╰\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m help: consider making this binding mutable: `mut `",
" \u001b[38;5;246m3 │\u001b[0m \u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;100mx\u001b[0m\u001b[38;5;100m \u001b[0m\u001b[38;5;100m=\u001b[0m\u001b[38;5;100m \u001b[0m\u001b[38;5;100m6\u001b[0m\u001b[38;5;100m6\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m┬\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m╰\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m cannot assign twice to immutable variable",
" \u001b[38;5;240m │\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;115mNote\u001b[0m: You can change an existing variable to mutable like: `let mut x = x;`",
"\u001b[38;5;246m───╯\u001b[0m"
]
},
{
"ename": "Error",
"evalue": "value assigned to `x` is never read",
"output_type": "error",
"traceback": [
"\u001b[31m[unused_assignments] Error:\u001b[0m value assigned to `x` is never read",
" \u001b[38;5;246m╭\u001b[0m\u001b[38;5;246m─\u001b[0m\u001b[38;5;246m[\u001b[0mcommand_8:1:1\u001b[38;5;246m]\u001b[0m",
" \u001b[38;5;246m│\u001b[0m",
" \u001b[38;5;246m2 │\u001b[0m \u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249ml\u001b[0m\u001b[38;5;249me\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;54m5\u001b[0m\u001b[38;5;54m5\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m─\u001b[0m\u001b[38;5;54m┬\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m╰\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m warning: value assigned to `x` is never read",
"\u001b[38;5;246m───╯\u001b[0m"
]
}
],
"source": [
"fn var3(){\n",
" let x = 55;\n",
" x = 66;\n",
" println!(\"Value of x is {}\",x); // Insert value in string, Version 2\n",
"}"
]
},
{
"cell_type": "markdown",
"id": "b390d673-bb49-45b0-afb2-2321178eeab5",
"metadata": {},
"source": [
"- Rust variables are **immutable** by default\n",
" - Like variables in mathematics\n",
" - Let $x = 4$ ... means $x$ is an arbitrary but fixed value\n",
"- Need to add a qualifier `mut` to say that a variable is mutable\n",
" - Notice the useful error message, suggesting that we add the qualifier `mut`"
]
},
{
"cell_type": "code",
"execution_count": 33,
"id": "54fac294-d3c1-4215-8faa-709f037b7826",
"metadata": {},
"outputs": [],
"source": [
"fn var4(){\n",
" let mut x = 55;\n",
" x = 66;\n",
" println!(\"Value of x is {}\",x); // Insert value in string, Version 2\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 34,
"id": "616bf90d-c1c0-43a6-a796-4bb35a976b1e",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of x is 66\n"
]
},
{
"data": {
"text/plain": [
"()"
]
},
"execution_count": 34,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"var4()"
]
},
{
"cell_type": "markdown",
"id": "4e723511-9521-4bdd-8b76-e86f43957349",
"metadata": {},
"source": [
"### Constants\n",
"- Immutable variables are not the same as constants\n",
"- Declare constants explicitly\n",
" - So far we have used implicit typing\n",
" - Constants need to be typed explicitly -- Rust uses older Algol/Pascal style `var: type` notation for typing rather than C/Java style `type var`\n",
" - Will describe Rust types shortly\n",
"- Constants can have *global* scope, declared outside all functions"
]
},
{
"cell_type": "code",
"execution_count": 35,
"id": "0ebf9ab5-5085-4f25-b461-fd9aeca2f313",
"metadata": {},
"outputs": [],
"source": [
"let x = 55;"
]
},
{
"cell_type": "code",
"execution_count": 36,
"id": "3ff995e2-b950-4942-ad8b-967882326074",
"metadata": {},
"outputs": [],
"source": [
"const PI_APPROX: f32 = 3.1415927;\n",
"fn const1(){ \n",
" println!(\"Value of pi is approximately {}\",PI_APPROX);\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 37,
"id": "096d814f-9b9c-4b89-b0da-7e83da651478",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of pi is approximately 3.1415927\n"
]
},
{
"data": {
"text/plain": [
"()"
]
},
"execution_count": 37,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"const1()"
]
},
{
"cell_type": "markdown",
"id": "9439d554-c0f2-4848-a212-04a3d2e98649",
"metadata": {},
"source": [
"### Shadowing\n",
"- Redeclaring a variable *shadows* the earlier definition\n",
"- Can change the type with each fresh declaration (but why?)"
]
},
{
"cell_type": "code",
"execution_count": 38,
"id": "9e13b1e8-98a7-4df9-9f2b-b44069f19452",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"value of x is 5\n"
]
}
],
"source": [
"let x = 0.0;\n",
"let x = 5;\n",
"println!(\"value of x is {}\",x);"
]
},
{
"cell_type": "markdown",
"id": "375134e6-de13-4827-8ecc-04187f67828b",
"metadata": {},
"source": [
"- But cannot change the type of a mutable variable"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "6d6e5773-ccde-4d5d-965b-e4add35ae9d3",
"metadata": {},
"outputs": [
{
"ename": "Error",
"evalue": "mismatched types",
"output_type": "error",
"traceback": [
"\u001b[31m[E0308] Error:\u001b[0m mismatched types",
" \u001b[38;5;246m╭\u001b[0m\u001b[38;5;246m─\u001b[0m\u001b[38;5;246m[\u001b[0mcommand_39:1:1\u001b[38;5;246m]\u001b[0m",
" \u001b[38;5;246m│\u001b[0m",
" \u001b[38;5;246m1 │\u001b[0m \u001b[38;5;249ml\u001b[0m\u001b[38;5;249me\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mm\u001b[0m\u001b[38;5;249mu\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;100m0\u001b[0m\u001b[38;5;100m.\u001b[0m\u001b[38;5;100m0\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m─\u001b[0m\u001b[38;5;100m┬\u001b[0m\u001b[38;5;100m─\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m╰\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m expected due to this value",
" \u001b[38;5;246m2 │\u001b[0m \u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;54m5\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m┬\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m╰\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m expected floating-point number, found integer",
"\u001b[38;5;246m───╯\u001b[0m"
]
},
{
"ename": "Error",
"evalue": "value assigned to `x` is never read",
"output_type": "error",
"traceback": [
"\u001b[31m[unused_assignments] Error:\u001b[0m value assigned to `x` is never read"
]
}
],
"source": [
"let mut x = 0.0;\n",
"x = 5;\n",
"println!(\"value of x is {}\",x);"
]
},
{
"cell_type": "markdown",
"id": "9a1bb0f7-dcbf-41f9-8ae4-c62d491ba484",
"metadata": {},
"source": [
"### Scalar types\n",
"- Signed integers: `i8`, `i32`, `i64`, `isize` -- explicitly specify number of bits, last version uses the underlying architecture default\n",
"- Unsigned integers: `u8`, `u32`, `u64`, `usize`\n",
"- Floats: `f32`, `f64`\n",
"- Boolean: `bool` --- values are `true` and `false`\n",
"- Charactre: `char` --- write with single quote, `'a'`, uses UTF-8, upto 4 bytes per character"
]
},
{
"cell_type": "markdown",
"id": "8a5d3fc3-c724-4d3b-b7b7-6f4501ac1d08",
"metadata": {},
"source": [
"- Implicit vs explicit typing\n",
" - Normally Rust deduces type from value assigned in `let`\n",
" - Can also explicitly annotate type"
]
},
{
"cell_type": "code",
"execution_count": 40,
"id": "af408ba9-0956-4570-a082-58dce48a5246",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of y is 12\n"
]
}
],
"source": [
"let mut y = 5.0;\n",
"let z = 7f32;\n",
"let y = y + z;\n",
"println!(\"Value of y is {}\",y);"
]
},
{
"cell_type": "markdown",
"id": "9be89643-3339-4354-a00c-b950bf605269",
"metadata": {},
"source": [
"- Strict typing\n",
" - Cannot have mixed int/float expressions --- use `as type` to \"recast\" a type\n",
" - Arithmetic expressions cannot replace boolean expressions -- convention that `0` is `false`, non-zero is `true` etc does not work"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "900cdf84-a219-4cfa-b07e-fd707ff2f95c",
"metadata": {},
"outputs": [
{
"ename": "Error",
"evalue": "cannot multiply `{float}` by `{integer}`",
"output_type": "error",
"traceback": [
"\u001b[31m[E0277] Error:\u001b[0m cannot multiply `{float}` by `{integer}`",
" \u001b[38;5;246m╭\u001b[0m\u001b[38;5;246m─\u001b[0m\u001b[38;5;246m[\u001b[0mcommand_41:1:1\u001b[38;5;246m]\u001b[0m",
" \u001b[38;5;246m│\u001b[0m",
" \u001b[38;5;246m2 │\u001b[0m \u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;54m*\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m7\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m┬\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m╰\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m no implementation for `{float} * {integer}`",
"\u001b[38;5;246m───╯\u001b[0m"
]
},
{
"ename": "Error",
"evalue": "value assigned to `x` is never read",
"output_type": "error",
"traceback": [
"\u001b[31m[unused_assignments] Error:\u001b[0m value assigned to `x` is never read"
]
}
],
"source": [
"let mut x = 5.8;\n",
"x = x * 7;\n",
"println!(\"Value of x is {}\",x);"
]
},
{
"cell_type": "code",
"execution_count": 57,
"id": "b809f458-11cf-41a2-bc1a-742e44f6ddea",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of x is 40.600002\n"
]
}
],
"source": [
"let mut x = 5.8;\n",
"x = x * 7 as f32;\n",
"println!(\"Value of x is {}\",x);"
]
},
{
"cell_type": "markdown",
"id": "847d31ea-7a95-4a49-b2fd-f3dbbef076a3",
"metadata": {},
"source": [
"### Defining functions\n",
"- Functions are defined using `fn`\n",
"- Need to provide explicit types for arguments and return value\n",
"- Notation for return value uses `->` like Haskell"
]
},
{
"cell_type": "code",
"execution_count": 58,
"id": "bf07448b-97ad-49cf-a582-9c7d31dfdd8d",
"metadata": {},
"outputs": [],
"source": [
"fn addtwo(x : i32, y: i32) -> i32 {\n",
" return x + y;\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 59,
"id": "17ddd4f6-2d4e-4237-a2ba-a97803a7a70a",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of a is 59\n"
]
}
],
"source": [
"let a = addtwo(17,42);\n",
"println!(\"Value of a is {}\",a);"
]
},
{
"cell_type": "markdown",
"id": "cc3d236d-ff7f-443e-8423-3d50a271c39c",
"metadata": {},
"source": [
"### Expressions\n",
"- Functions implicitly return last *expression* evaluated\n",
"- Can rewrite our function as below"
]
},
{
"cell_type": "code",
"execution_count": 60,
"id": "56a53e80-3cec-42fc-b6ed-9ccb7c6ad3f2",
"metadata": {},
"outputs": [],
"source": [
"fn addtwoexpr(x : i32, y: i32) -> i32 {\n",
" x + y\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 61,
"id": "99b23a31-44dd-480c-8e48-2ca37e8a3c27",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Value of a is 59\n"
]
}
],
"source": [
"let a = addtwoexpr(17,42);\n",
"println!(\"Value of a is {}\",a);"
]
},
{
"cell_type": "markdown",
"id": "20121836-394d-458d-bf77-d2fedf170f5c",
"metadata": {},
"source": [
"- An expression should not have a semicolon at the end\n",
"- Semicolon turns the expression into a *statement*\n",
" - Note again the helpful compiler error message"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "31bedd86-be9a-40d9-ba35-901f91b1cc8f",
"metadata": {},
"outputs": [
{
"ename": "Error",
"evalue": "mismatched types",
"output_type": "error",
"traceback": [
"\u001b[31m[E0308] Error:\u001b[0m mismatched types",
" \u001b[38;5;246m╭\u001b[0m\u001b[38;5;246m─\u001b[0m\u001b[38;5;246m[\u001b[0mcommand_62:1:1\u001b[38;5;246m]\u001b[0m",
" \u001b[38;5;246m│\u001b[0m",
" \u001b[38;5;246m1 │\u001b[0m \u001b[38;5;249mf\u001b[0m\u001b[38;5;249mn\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;100ma\u001b[0m\u001b[38;5;100md\u001b[0m\u001b[38;5;100md\u001b[0m\u001b[38;5;100mt\u001b[0m\u001b[38;5;100mw\u001b[0m\u001b[38;5;100mo\u001b[0m\u001b[38;5;100ms\u001b[0m\u001b[38;5;100me\u001b[0m\u001b[38;5;100mm\u001b[0m\u001b[38;5;100mi\u001b[0m\u001b[38;5;100mc\u001b[0m\u001b[38;5;100mo\u001b[0m\u001b[38;5;100ml\u001b[0m\u001b[38;5;100mo\u001b[0m\u001b[38;5;100mn\u001b[0m\u001b[38;5;249m(\u001b[0m\u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m:\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mi\u001b[0m\u001b[38;5;249m3\u001b[0m\u001b[38;5;249m2\u001b[0m\u001b[38;5;249m,\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249my\u001b[0m\u001b[38;5;249m:\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mi\u001b[0m\u001b[38;5;249m3\u001b[0m\u001b[38;5;249m2\u001b[0m\u001b[38;5;249m)\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m-\u001b[0m\u001b[38;5;249m>\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;54mi\u001b[0m\u001b[38;5;54m3\u001b[0m\u001b[38;5;54m2\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m{\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m┬\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m \u001b[38;5;54m─\u001b[0m\u001b[38;5;54m┬\u001b[0m\u001b[38;5;54m─\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m╰\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m implicitly returns `()` as its body has no tail or `return` expression",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m│\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m╰\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m expected `i32`, found `()`",
" \u001b[38;5;246m2 │\u001b[0m \u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mx\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m+\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249my\u001b[0m\u001b[38;5;68m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;68m┬\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;68m╰\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m help: remove this semicolon to return this value: ``",
"\u001b[38;5;246m───╯\u001b[0m"
]
},
{
"ename": "Error",
"evalue": "value assigned to `x` is never read",
"output_type": "error",
"traceback": [
"\u001b[31m[unused_assignments] Error:\u001b[0m value assigned to `x` is never read"
]
}
],
"source": [
"fn addtwosemicolon(x : i32, y: i32) -> i32 {\n",
" x + y;\n",
"}"
]
},
{
"cell_type": "markdown",
"id": "077e3de7-1495-4e74-bd38-ca7c0ce04bba",
"metadata": {},
"source": [
"### Control flow\n",
"- `if` boolean-expression `{ ... } else {....}`\n",
"- loops: `while` boolean-expression `{...}`, `loop {...}`, `for`\n",
"- `loop` requires a `break`, else infinite\n",
"- `for` runs over elements from an iterator --- later"
]
},
{
"cell_type": "code",
"execution_count": 63,
"id": "4f8ea2e8-984c-42ec-9560-9cc6b15a0af6",
"metadata": {},
"outputs": [],
"source": [
"fn signum1(x: i32) -> i32{\n",
" if x < 0 {return -1;}\n",
" else if x == 0 {return 0;}\n",
" else {return 1;}\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 64,
"id": "46979d5b-db05-484f-9fd5-b8d86e238fe2",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"-1"
]
},
"execution_count": 64,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"signum1(-7)"
]
},
{
"cell_type": "markdown",
"id": "6aaa7dce-a169-490c-97b1-3faf1778a603",
"metadata": {},
"source": [
"- `if` is itself an expression, so can do a conditional assignment"
]
},
{
"cell_type": "code",
"execution_count": 65,
"id": "0002033c-930b-441f-8316-5b865e8121da",
"metadata": {},
"outputs": [],
"source": [
"fn signum2(y: i32) -> i32{\n",
" let x = if y < 0 {-1} else if y == 0 {0} else {1};\n",
" return x;\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 66,
"id": "abf3dce2-281b-42c3-b77f-a4e9054a1807",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"0"
]
},
"execution_count": 66,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"signum2(0)"
]
},
{
"cell_type": "markdown",
"id": "8162a392-f0f6-48d6-b570-685f9a11a435",
"metadata": {},
"source": [
"- This cryptic `if` expression suffices"
]
},
{
"cell_type": "code",
"execution_count": 67,
"id": "eef88e5b-07c7-4558-be12-6c70842b50cf",
"metadata": {},
"outputs": [],
"source": [
"fn signum3(y: i32) -> i32{\n",
" if y < 0 {-1} else if y == 0 {0} else {1}\n",
"}"
]
},
{
"cell_type": "code",
"execution_count": 68,
"id": "c716c08c-ef36-4923-a9a8-6ee1c17cddd3",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"1"
]
},
"execution_count": 68,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"signum3(77)"
]
},
{
"cell_type": "markdown",
"id": "032bbecc-d0f1-4176-b3dd-4ba2c5cce098",
"metadata": {},
"source": [
"### Copying values\n",
"- `x = y` for values stored on the stack copies the value\n",
"- `x = y` for values stored on the heap creates an *alias* -- both `x` and `y` refer to the same value on the heap\n",
" - Useful to avoid copying large values, and to pass heap objects to a function\n",
" - However, leads to subtle errors because updating `y` indirectly updates `x`\n",
" - Also, releasing memory through `y` results in a *dangling pointer* at `x`\n",
"- Rust introduces a concept called **ownership** to address these issues"
]
},
{
"cell_type": "markdown",
"id": "74ed093b-e17f-40bd-b42b-71cfb3b25898",
"metadata": {},
"source": [
"### Strings\n",
"- Stored on the heap"
]
},
{
"cell_type": "code",
"execution_count": 69,
"id": "83190f61-a6ac-49bf-bfa8-e310fcde0775",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"hello, world!\n",
"Again hello, world!\n"
]
}
],
"source": [
"let mut s = String::from(\"hello\"); // allocates heap space for new String and initializes\n",
"s.push_str(\", world!\"); // push_str() appends a literal to a String\n",
"println!(\"{}\", s); // This will print `hello, world!`\n",
"println!(\"Again {}\",s);"
]
},
{
"cell_type": "markdown",
"id": "84b6d417-3f57-42b1-9754-53801e9c7390",
"metadata": {},
"source": [
"### Copying values, stack\n",
"- Value is copied"
]
},
{
"cell_type": "code",
"execution_count": 70,
"id": "70980753-b77b-48aa-9e43-6e6d212a43ed",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"x = 7, y = 77\n"
]
}
],
"source": [
"let mut x = 7;\n",
"let mut y = x;\n",
"y = 77;\n",
"println!(\"x = {}, y = {}\",x,y);"
]
},
{
"cell_type": "markdown",
"id": "217225f8-96c1-47e3-bf80-785319dd516e",
"metadata": {},
"source": [
"### Copying values, heap\n",
"- Every value on the heap has a unique owner\n",
"- Assignment *moves* ownership\n",
"- Memory is freed as soon as scope of owner ends"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "e359975c-7683-4ba2-a292-7dd1f2ed53d7",
"metadata": {},
"outputs": [
{
"ename": "Error",
"evalue": "value assigned to `x` is never read",
"output_type": "error",
"traceback": [
"\u001b[31m[unused_assignments] Error:\u001b[0m value assigned to `x` is never read"
]
},
{
"ename": "Error",
"evalue": "borrow of moved value: `s1`",
"output_type": "error",
"traceback": [
"\u001b[31m[E0382] Error:\u001b[0m borrow of moved value: `s1`",
" \u001b[38;5;246m╭\u001b[0m\u001b[38;5;246m─\u001b[0m\u001b[38;5;246m[\u001b[0mcommand_71:1:1\u001b[38;5;246m]\u001b[0m",
" \u001b[38;5;246m│\u001b[0m",
" \u001b[38;5;246m1 │\u001b[0m \u001b[38;5;249ml\u001b[0m\u001b[38;5;249me\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;68mm\u001b[0m\u001b[38;5;68mu\u001b[0m\u001b[38;5;68mt\u001b[0m\u001b[38;5;68m \u001b[0m\u001b[38;5;68ms\u001b[0m\u001b[38;5;68m1\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mS\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249mr\u001b[0m\u001b[38;5;249mi\u001b[0m\u001b[38;5;249mn\u001b[0m\u001b[38;5;249mg\u001b[0m\u001b[38;5;249m:\u001b[0m\u001b[38;5;249m:\u001b[0m\u001b[38;5;249mf\u001b[0m\u001b[38;5;249mr\u001b[0m\u001b[38;5;249mo\u001b[0m\u001b[38;5;249mm\u001b[0m\u001b[38;5;249m(\u001b[0m\u001b[38;5;249m\"\u001b[0m\u001b[38;5;249mh\u001b[0m\u001b[38;5;249me\u001b[0m\u001b[38;5;249ml\u001b[0m\u001b[38;5;249ml\u001b[0m\u001b[38;5;249mo\u001b[0m\u001b[38;5;249m\"\u001b[0m\u001b[38;5;249m)\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m┬\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;68m╰\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m\u001b[38;5;68m─\u001b[0m move occurs because `s1` has type `String`, which does not implement the `Copy` trait",
" \u001b[38;5;246m2 │\u001b[0m \u001b[38;5;249ml\u001b[0m\u001b[38;5;249me\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249mm\u001b[0m\u001b[38;5;249mu\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249ms\u001b[0m\u001b[38;5;249m2\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;54ms\u001b[0m\u001b[38;5;54m1\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m─\u001b[0m\u001b[38;5;54m┬\u001b[0m\u001b[38;5;37m│\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;54m╰\u001b[0m\u001b[38;5;54m─\u001b[0m\u001b[38;5;54m─\u001b[0m value moved here",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;37m│\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;37m╰\u001b[0m\u001b[38;5;37m─\u001b[0m help: consider cloning the value if the performance cost is acceptable: `.clone()`",
" \u001b[38;5;240m │\u001b[0m ",
" \u001b[38;5;246m4 │\u001b[0m \u001b[38;5;249mp\u001b[0m\u001b[38;5;249mr\u001b[0m\u001b[38;5;249mi\u001b[0m\u001b[38;5;249mn\u001b[0m\u001b[38;5;249mt\u001b[0m\u001b[38;5;249ml\u001b[0m\u001b[38;5;249mn\u001b[0m\u001b[38;5;249m!\u001b[0m\u001b[38;5;249m(\u001b[0m\u001b[38;5;249m\"\u001b[0m\u001b[38;5;249ms\u001b[0m\u001b[38;5;249m1\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m{\u001b[0m\u001b[38;5;249m}\u001b[0m\u001b[38;5;249m,\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249ms\u001b[0m\u001b[38;5;249m2\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m=\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249m{\u001b[0m\u001b[38;5;249m}\u001b[0m\u001b[38;5;249m\"\u001b[0m\u001b[38;5;249m,\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;100ms\u001b[0m\u001b[38;5;100m1\u001b[0m\u001b[38;5;249m,\u001b[0m\u001b[38;5;249m \u001b[0m\u001b[38;5;249ms\u001b[0m\u001b[38;5;249m2\u001b[0m\u001b[38;5;249m)\u001b[0m\u001b[38;5;249m;\u001b[0m",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m─\u001b[0m\u001b[38;5;100m┬\u001b[0m ",
" \u001b[38;5;240m │\u001b[0m \u001b[38;5;100m╰\u001b[0m\u001b[38;5;100m─\u001b[0m\u001b[38;5;100m─\u001b[0m value borrowed here after move",
"\u001b[38;5;246m───╯\u001b[0m"
]
}
],
"source": [
"let mut s1 = String::from(\"hello\");\n",
"let mut s2 = s1;\n",
"s2.push_str(\", world\");\n",
"println!(\"s1 = {}, s2 = {}\", s1, s2); "
]
}
],
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"kernelspec": {
"display_name": "Rust",
"language": "rust",
"name": "rust"
},
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"codemirror_mode": "rust",
"file_extension": ".rs",
"mimetype": "text/rust",
"name": "Rust",
"pygment_lexer": "rust",
"version": ""
}
},
"nbformat": 4,
"nbformat_minor": 5
}